Computer generated image of relatively prime integers and zeta(2)

Relatively prime integers and zeta(2): The red dots are the coprime pairs of integers (x,y) with distance at most N (N = 20 in this picture) from the origin. They are connected to the origin by non-overlapping rays. The blue dots are all pairs of integers in the same disk. Their ratio tends to 1/zeta(2) = 6/pi^2 as N tends to infinity, where zeta(s) is the Riemann zeta funtion Sum_n (1/n^s). (Image by Prof. Abhinav Kumar.)